In a process of manufacturing a semiconductor element device, in order to detect the generation of abnormality or generation of failure in lithography processing, etching processing and other processing early or in advance, inspection of a pattern on a semiconductor wafer is carried out at the end of each manufacturing process.
With the miniaturization of circuit patterns, the complication of circuit pattern shapes, and the diversification of materials, a method and device for inspecting a pattern using an electron beam image with a higher resolution than an optical image is put into practical use.
In order to carry out high-throughput and highly accurate inspection to catch up with the increase in wafer diameter and the miniaturization of circuit patterns, it is important to acquire a high-SN image at a very high speed.
Patent Document 1 discloses an invention in which, in order to carry out beam canning at a high speed and with high accuracy, scanning deflection control is processed in a divided manner in a high-speed circuit and a low-speed circuit and data transmission and a synchronizing method between the high-speed circuit and the low-speed circuit are contrived, thus enabling high-speed high-accuracy data calculation processing.
Here, since an electronic beam is cast onto an inspection target in order to obtain an electron beam image, the inspection target becomes charged (charged-up). However, depending on charging state, it is difficult in some cases to obtain an image with stable luminance and predetermined inspection accuracy in an inspection with electron beams.
When the charging in the inspection target is generated, there is a problem that the generation efficiency of secondary electrons from the generating part falls or the trajectory of secondary electrons after the generation is affected, thus causing change in brightness/darkness of the image and also causing the image to be distorted without reflecting the actual shape of the circuit pattern.
Moreover, this charging state is sensitive to irradiation conditions of the electron beam. If the irradiation speed or irradiation range of the electron beam is changed, the image ends up with totally different contrast even with respect to the same circuit pattern in the same position.
In the case where a narrowed thin electron beam with small electron beam current is slowly cast onto a sample and signal detection is carried out over a long time, as in the conventional SEM, a signal detected during a detection time per unit pixel is integrated to form an image signal of that unit pixel, in order to obtain a necessary SN ratio for comparative inspection. Since the charging state changes with time depending on irradiation time, as described already, the image signal changes while being integrated, making it difficult to obtain stable contrast. It is necessary to restrain the influence of temporal change due to charging.
FIG. 1 is a view showing the relation between the scanning time and waiting time of an electron beam 19 and the position in X direction. In FIG. 1, a scanning time T1 is considered an irradiation interval between scanning (1) and scanning (2), and a canning time T2 is considered an irradiation interval between scanning (2) and scanning (3). When a scanning time T3 is controlled fixedly, waiting times T4 and T5 for each irradiation are made even by scanning in such a manner that T1 and T2 become the same duration. By thus making the irradiation interval constant, the charging status can be made uniform and the generation of uneven contrast can be restrained.
Also, by making the amount of Y deflection constant, correction processing for focal distortion due to deflection to Y direction, processing of out-of-deflection field determination or the like are no longer necessary, and the simplification of processing improves reliability and processing speed and can contribute to improvement in throughput.